Zodarion spiders dine exclusively on ants, and they're very particular about how those ants should be prepared. The spiders always eat the ants' heads first. It turns out this ghoulish practice is vital for the spider's survival.

A group of researchers wanted to see of Zodarions simply thought the heads were tastier, or if the preference for heads served a purpose. So they devised a culinary experiment for their arachnid gourmands. According to Live Science:

These spiders attack ants and inject them with powerful venom that paralyzes the prey in mere minutes.

When settling in for an ant banquet, Zodarion spiders puncture the insects' hard exoskeletons with fangs and inject enzymes that "liquefy the inner tissues," Pekár said. The spiders slurp out this mush before moving to different areas of the carcass. These spider eating sessions last from two to four hours.

To see how well the spiders lived on particular pieces of an ant, the researchers divided 60 of the arachnids into three dining clubs that were given the ants' front end (head, legs and thorax or mid-body), gasters or whole ants. Each group received a similar portion of fresh ant flesh by weight.

The spiders given only gasters fared poorly: All 20 died within six weeks of the start of the experiment, whereas eight of the spiders dining on front parts and three on whole ants were still alive and kicking at the experiment's end three months later.

When alive, the spiders kept on the gaster-only diet initially grew but then shriveled, while those eating the head, legs and thoraces thrived, with some tripling their weight. The spiders devouring entire ants also did well, but did not develop as fast or get as big as the front-end eaters.

So there you have it. Picky eaters may be the perfect products of evolutionary selection.